Various types of fluid flow control valves are used in applications where the valve internals are subjected to corrosive acidic or caustic liquids, or where the purity of the liquids which flow through the valve must be maintained. An example of such application is the semi-conductor manufacturing industry where process chemicals distributed through a control valve must maintain a high degree of chemical purity to avoid contamination that may occur on the microscopic level. Such valves are either constructed of relatively inert materials, e.g., fluoropolymers or other polymeric materials, or the valve surfaces which come into contact with the flowing liquids or which potentially can come into contact with the liquids, are coated with such inert materials.
Fluid flow control valves known in the art are commonly biased into the closed position by a spring force and are opened by means of a solenoid actuator, or actuator means operated by pneumatic or hydraulic pressure and the like. Valve closure springs typically used in such valves are made from a metallic material and configured to afford a resilient action. Such fluid control valves also include at least one, and more commonly two diaphragms disposed within the valve chamber of the valve. Each diaphragm is placed into contact with the fluid and serves to prevent the escape of the fluid from the valve chamber into the valve operating mechanism and into the environment. A valve stem is disposed axially within the chamber and each diaphragm is attached to an opposite end of the valve stem. Each diaphragm comprises a peripheral edge portion that is engaged against an adjacent wall portion of the valve body at each opposite end of the valve body.
The valve closure springs are typically placed adjacent a surface of the valve diaphragm that is not exposed to the process fluid distributed through the valve. The distribution of the process fluid through the valve is controlled by the actuation of the valve stem within the chamber against valve seats. The movement of the valve stem is accommodated in part by the controlled deformation of the diaphragms. Control valves constructed in this manner are prone to failure due to both the possibility of eventual diaphragm rupture and to the large number of leak paths inherent in such construction. A valve constructed in this manner has four leak paths or potential passages through which fluid within the valve chamber can escape into the valve operating mechanism or the environment. Two leak paths comprise the attachment points between the diaphragms and each opposite end of the valve stem, and the other two leak paths comprise the seal between the peripheral edge of each diaphragm and the valve body walls.
Diaphragm rupture or leakage though any one of the leak paths is not desirable because the process chemical directed through the valve chamber may be allowed to escape into the valve body where the corrosive or caustic chemical can come into contact with the valve springs, and thereby provide a source of ionic contamination to the process chemical to pass on to other downstream chemical processing units. Alternatively, diaphragm rupture or leakage may result in the escape of the process chemical from the valve chamber, through the valve body and onto the ground or into the atmosphere, where the particular process chemical may cause a hazard to the environment or a health danger to nearby operators.
U.S. Pat. No. 3,329,165 discloses a solenoid-operated multi-way valve comprising an actuating rod that extends through a poppet valve element. The poppet valve element is disposed axially within a central valve chamber in communication with three liquid ports. The central valve chamber is formed from a valve body made up of four stacked valve body members held in place by a screw type fastener. The poppet valve element comprises two coaxial conical faces that are arranged between opposing valve seats within the valve chamber. The axial movement of the valve poppet element within the valve chamber controls the flow of liquid through the valve to two of the three valve ports, depending on whether the poppet is in communication with one or the other valve seat. The valve comprises metallic sealing rings at deformable diaphragm-like portions of the valve poppet at opposite ends to secure each valve poppet end to adjacent portions of the valve body.
The valve design of the above-referenced patent reduces the number of leak paths between the poppet valve element and the valve chamber to two, one at the interface between each deformable end portion of the valve poppet and the adjoining valve body. However, the design of using multiple valve body members to form the valve body and the valve chamber presents additional leak paths between adjoining valve body members that does not minimize the possibility of chemical leakage from the valve chamber into the environment. There also still exists the possibility for the introduction of ionic contamination into the chemical process upon failure of the poppet valve element by exposure of the leaking process chemical with the metal ring elements.
Additionally, the construction of such a valve requires a large amount of machining in order to configure the valve chamber, valve seats, and valve ports, thereby increasing the amount of time and labor needed to produce the valve and, thus increasing the cost of the valve as well.
In the handling of fluids where the chemical purity must be maintained to ensure the desired degree of quality for the product manufactured using such process fluids, it is desired that the fluid control valve be made in a manner that eliminates the possibility that contaminants may be introduced into the process caused by contact of the process fluid with elements of the valve during distribution therethrough. It is, therefore, desirable to provide a flow control valve for use in the distribution of process fluids or gases where a high degree of chemical purity is desired that will not introduce contamination into the process. It is desirable that the valve be made from material having a high degree of chemical resistance and thermal resistance to resist degradation through contact with corrosive or caustic chemicals and the like. It is desirable that the valve be constructed in a manner that results in the inherent reduction of leak paths, thereby minimizing the potential for chemical leakage into the environment. It is desirable that the valve be capable of operating at high temperatures and under high pressures without danger of valve failure or chemical leakage. It is also desirable that the valve is constructed using conventional manufacturing principles from available materials to reduce the cost of manufacturing such valve.